Power Conundrum - Low end ok, high end blech (1 Viewer)

[gifu]

1986 FJ60 low power in high RPM

background:
engine was (ostensibly) rebuilt about 15K miles ago.
when I bought this rig, it barely idled.

my background:
I'm a pretty dang good shade tree mechanic. Over 20+ years of cruiser ownership... I've done dozen engine conversions, rebuilt motors, owned 60+ cruisers.
(i've been going to this high school for 6 years... I'm no dumby)
I'm f***ing stumped.

work done:
rebuilt carb
new fuel filter
tripled checked emissions layout (it was a mess, explains why it wouldn't idle.)
adjusted valves
new cap, rotor, plugs
tested vacuum advance
timing set
HAC operational
tested wires
heat riser operational
compression check (not perfect.. but dang not bad)

Now, it starts easy (I'm at 6200', it's winter)
it idles great.
it has fine power right off the line... till about 1800... then peters out

... it will NOT push pass 2800rpm or so.
2nd gear.. floored... FLOORED... FUH-LOORED.... in my neighborhood, small hill... it will BARELY get to 2600 rpm.
I have another FJ60 here, it drives great up the same small hills...

hair: pulled out
brain: imploded
Me: stumped

only thing I haven't tried is cutting out the catalytic converter (but it looks newish?)

I'm at the end of my rope. Help me Obi Wan Kenobi!

 

[3_puppies]

fuel flow issue?

 

[mattressking]

Timing set to what? You verified HAC is functioning because you vacuum tested the advance unit/verified the HAC is bumping timing up at your altitude? What is your vacuum at idle?

Is your vacuum secondary working? Have you done the paper clip test to make sure it's actuating? 1800rpm is when things start shifting, have you bypassed the egr to see if that changes operation? If the idle is smooth, not misfiring and you verified that by testing each cylinder then my assumption is that it's something carb/vacuum related. Fuel is in middle of sight glass on carb?

 

[lndshark]

Exhaust restriction. Easy check with a vacuum gauge.

 

[FJ40Jim]

If centrifugal advance is stuck, engine will flatten out with RPM.

 

[micruz60]

Compare the linkage from pedal to carburetor with the other 60?

Advance the timing to see if that helps?

As mentioned above, paperclip test on secondary.

HTH

 

[Seth S]

My first thought was that this sounds normal given that a 2f makes all its power down low and doesn’t really have a high end

 

[OSS]

When stopped and out of gear, can the engine be slowly brought up to 3200 rpm easily and held there for a short while?

If not - I'm guessing ignition problem
If yes - I'm guessing fuel delivery problem

 

[gifu]

great ideas guys!

How do I check plugged exhaust with a vacuum gauge?

yes the HAC works. vacuum at idle is about 13 inches.
Timing is at stock, but i'll bump it up for s***s and giggles.
I can rev engine in neutral to 3500+

OK so... today I will:
check timing at 2500 rpm (should be quite advanced right?)
do paperclip test on secondary vacuum (have had carb off twice since rebuild to check secondary etc)
If paperclip fails, will borrow rebuilt carb from my friend Karl.
if other carb has no change, will try a new fuel pump

anything else? remove engine, install 1HDT???

 

[FJ40Jim]

Late reply:
Plugged exhaust will show as poor vacuum when engine held at higher RPM.

Centrifugal Timing should be ~12° advanced by 2500, maxing at 21° at 3800.

 

[gifu]

Aaaaaaaaand the final answer was plugged cat!!! Hahaha. Dang that was a long road to figure it all out.

 

[cheeese]

Well, at least it's nothing else wrong with the motor…

 

[gifu]

Right? Never been so relieved to find something wrong.

 

[DFXR]

That's good news in its own weird way. Bummer is that Cats are expensive as all heck right now.